Fast Meters Scale Microwave Power Peaks

These compact but powerful power meters measure both peak and CW power levels through millimeter-wave frequencies at power levels as low as -70 dBm.

Power measurements are critical for characterizing modern high-frequency systems and their components. With the growing use of pulsed and pseudorandom signals in both commercial communications and military radar systems, power meters capable of peak and continuous-wave (CW) measurements are more valuable than ever The new 4540 series of power meters from Boonton Electronics (www.boonton.com) is such an instrument, working with a wide range of the company's power sensors and providing extensive peak and CW power measurement capabilities at frequencies from 1 MHz through 110 GHz depending upon choice of sensor. The 4540 series power meters, which are available as single-channel (model 4541) and dualchannel (model 4542) units, boast a wide range of external triggering functions, statistical measurements, and automated measurements to understand peak and pulsed power levels.

The 4540 series power meters are designed for measuring the power levels of real-world CW/modulated, and pulsed signals, which rarely have ideal rectangular shapes. Their pulsed measurement capabilities make it possible to measure and analyze different increments of a pulse, from rise time to falltime, using cursors and triggers to capture information about different portions of a pulsed signal. The minimum singleshot time for a pulsed event is 200 ns.

One of the first things that stands out about a 4540 power meter (Fig. 1) is the vivid display screen for such a compact instrument, a 4-in. color thinfilm- transistor (TFT), liquid-crystaldisplay (LCD) screen with 320 x 240 pixel resolution. That clear display can show as many as 15 time- or powerbased measurements per channel simultaneously. The 4540 can also drive an external VGA, SVGA, or XVGA monitor to 320 x 240 pixel resolution by means of a rear-panel VGA output port.

A 4540 peak power meter offers a maximum power measurement range of -50 to +20 dBm for peak power and -70 to +44 dBm for CW power, dependent on the connected sensor. The power meter provides a relative offset range of 100.00 dB. The meter works with a wide assortment of the company's CW and peak power sensors, including the models 57518 and 57540 with frequency ranges of 0.1 to 18.0 GHz and 0.1 to 40.0 GHz, respectively. Each sensor supports peak power measurements from -40 to +20 dBm and CW power measurements from -50 to +20 dBm (see Table 1).

In support of power measurements on pulsed and modulated signals, the 4540 features video bandwidth of 70 MHz with a single-shot bandwidth of 5 MHz (based on 10 samples/pulse) and rise time of 7 ns for capturing the power levels of short radar pulses and the pseudorandom, noise-like signals commonly found in modern communications systems. The 4540 brings very capable signal-acquisition circuitry to the power measurements, based on a 14-bit analog-to-digital converter (ADC) with 0.2-ns time resolution and a 32-bit floating-point digital signal processor (DSP) for advanced mathematical and statistical processing.

The 4540 peak power meters can work with external trigger signals over a range of -5 to +5 V to capture the power levels and other characteristics of pulsed and modulated test signals. Triggering can occur at a minimum trigger pulse width of 15 ns and maximum trigger rate of 30 MHz to capture leading and trailing edges of pulses and even characterize the power flatness across a pulse width. Markers can be set in time relative to the trigger position or independently for measuring power at specific times, such as average, peak, and minimum power. In addition, a pair of markers can be used to measure power at two specified times with a ratio or average power between them, the minimum or maximum power between them, the ratio of average power between them, the peak power between them, or the peak-to-average power between the markers.

The statistical-mode analysis helps more accurately evaluate signals that have pseudorandom characteristics, such as code-division-multiple-access (CDMA) and orthogonal-frequencydivision- multiplex (OFDM) signals in cellular and WiMAX systems, respectively. This measurement mode uses statistical functions such as complementary cumulative distribution functions (CCDFs) to analyze signal power based on the probability that the power is greater than a specific value. CCDF-based analysis can be used to determine optimum transmitter output power for a given system bit-error rate (BER). The CCDF is also useful for evaluating different modulation schemes in order to determine the stress of different formats on linear amplifiers and transmitters.

The modulated measurement mode is suitable for signals that show repeating patterns. It is a continuous measurement mode and does not differentiate between the times a pulsed or periodic signal is off and the times it is on. It is best when used for signals with continuous modulation at a modulation bandwidth less than 20 MHz. This measurement mode allows an operator to set filter parameters for detecting the power levels of modulated signals, or use an autodetection function to make modulated-signal power measurements.

To maintain a high level of accuracy in all three measurement modes, the 4540 peak power meter has a built-in 50-MHz calibrator that provides precisely known power levels from -60 to +20 dBm in 0.1-dB steps. The calibrator's signals are available from a frontpanel port. In addition, the 4540 peak power meter can also use an external source for calibration.

In many ways, the 4540 peak power meter can be thought of as a "poor man's" version of the 4500B, the company's flagship power analyzer (see Table 2). Both instruments work with most of the same CW and peak power sensors, and both offer comprehensive time-domain and statistical-domain measurement capabilities. The 4540 meters cover a sensor-dependent frequency range of 1 MHz to 110 GHz while the 4500B analyzer spans 1 MHz to 40 GHz, again depending upon the attached sensor.

The 4540 peak power meter measures 8.2 x 3.5 x 16.5 in. (20.8 x 8.9 x 34.3 cm) in a 2U-high, half-rackspace enclosure and weighs 7.7 lbs (3.5 kg). It conforms to European Union (EU) specifications EN 61010-1(90) (+A1/92)(+A2/95), EN 61010-2-031, EN 61326-1(97), and EN 55022(94) A2/(97) Class B environmental specifications. The meters are manufactured to the intent of MIL-T28800E, Type III, Class 5, Style E military specifications. The 4540 can be ordered with the measurement channel or channels and the calibrator output mounted on the rear panel, which may be preferred for ATE installations. The 4540 offers flexible remote control and computer interface connections, with built-in General Purpose Interface Bus (GPIB), Universal Serial Bus (USB), and Ethernet local area network (LAN) ports.

The 4540 is designed for operating temperatures from 0 to +50C. It incorporates a secure mode for sensitive installations that require safeguardig of data. In this mode, the power meter automatically erases all test settings and data after a measurement session. Its powerful measurement capabilities are tempered by its interactive graphical user interface, readable screen, and automated measurements to simplify advanced power measurements on modulated signals. P&A: $8,345 (single-channel model 4541) and $9,985 (dual-channel model 4542); 30 days. Boonton Electronics, a Wireless Telecom Group Company, 25 Eastmans Rd., Parsippany, NJ 07054-3702; (973) 386-9696, FAX: (973) 386-9191, e-mail: boonton@boonton.com, Internet: www.boonton.com.